Enable version switcher in local build

Author: AlenkaF

dev/tasks/tasks.yml

@@ -1215,6 +1215,7 @@ tasks:
     params:
       env:
         JDK: 17
+        DOCS_DEV: "1"
       pr_number: Unset
       image: debian-docs
       publish: true

docs/source/conf.py

@@ -328,6 +328,15 @@
 # documentation.
 #
 
+# To enable the version switcher during a local build, set the
+# environment variable DOCS_DEV to "1".
+docs_dev = os.environ.get("DOCS_DEV", "0")
+json_url = "/docs/_static/versions.json"
+
+if docs_dev == "1":
+    json_url = "https://arrow.apache.org/docs/_static/versions.json"
+    # json_url = "_static/versions.json"
+
 switcher_version = version
 if ".dev" in version:
     switcher_version = "dev/"
@@ -365,7 +374,7 @@
     ],
     "show_version_warning_banner": True,
     "switcher": {
-        "json_url": "/docs/_static/versions.json",
+        "json_url": json_url,
         "version_match": switcher_version,
     },
 }

docs/source/developers/documentation.rst

@@ -87,6 +87,12 @@ These two steps are mandatory and must be executed in order.
    not sufficiently comprehensive. Portions of the Python API documentation
    will also not build without CUDA support having been built.
 
+.. note::
+
+   To enable the version switcher in a local documentation build, set the
+   environment variable ``DOCS_DEV=1`` before building, or run the build
+   command with it inline, for example: ``DOCS_DEV=1 make html``.
+
 After these steps are completed, the documentation is rendered in HTML
 format in ``arrow/docs/_build/html``.  In particular, you can point your browser
 at ``arrow/docs/_build/html/index.html`` to read the docs and review any changes